The increasing need for miniaturization of electronic systems has stimulated the development of thin films for microelectronics and, in particular, thin film dielectrics that have a variety of applications varying from protective coatings to energy storage devices in the form of capacitors. Organic/polymer materials utilized in films have shown very attractive dielectric, optical and mechanical properties because they have relatively high strength and undergo elastic deformation when forces are applied so as to minimize stresses in the film structure.
When thin film dielectrics are utilized as a charge storage device such as in a capacitor structure, the specific capacitor structure in conjunction with the properties of the material used to form the capacitor structure serve to define the characteristics and usefulness of the capacitor. This is particularly important in the market environment that presently exists in which miniaturization of the capacitor is desired whereby high capacitance value per unit volume is an important parameter when developing new dielectric systems. Similarly, when films are to be utilized as a protective coating or a dielectric, it is paramount that the film be delamination free, pin hole free and void free.
Further, it is important not only to have a thin, multi layer, solid film with the desired physical, chemical and, depending upon the application, electrical or optical properties, but also, it is imperative that the multi layer film, which in certain applications comprises 5,000 layers, be produced at a rate that is commercially attractive. For example, in British Patent No. 1,168,641 a process is disclosed for producing coatings on metal substrates. The system disclosed, however, is not particularly satisfactory for commercial purposes in many applications because the rate at which the film is manufactured is too slow and/or it appears that it will produce a structure that is not satisfactory.
It is an object of the present invention to provide a thin film, multi layer polymer article which can be produced relatively economically and at a relatively high speed of production. The multi layer structure is monolithic in nature in that multiple dielectric or dielectric and interleaved metal or other inorganic material layers can be formed in a single structure that is cohesive and free of air layers.
It is further an object of the present invention to provide a multi layered structure that has mechanical and electrical properties which are useful in a variety of applications that make use of multiple dielectric layers and/or dielectric and metal layers interleaved in various combinations such as to allow an electrical charge to be stored, electromagnetic radiation to be reflected or other properties of the multi layered structure to be utilized for a particular application.
One particular application of a multi layer film relates to capacitors. A monolithic capacitor is one in which the layers of electrodes and dielectric are bonded together in a unitary structure as opposed, for example, to a metallized film capacitor in which self-supporting films are rolled or wound into the capacitor form. A miniaturized capacitor is one of very small dimensions so as to be suitable for microcircuitry. Small overall size could denote low capacitance of little practical value, except that the thickness of the intervening dielectric layer inversely affects the capacitance between adjacent electrodes, and the number of electrode pairs directly affects capacitance. Therefore, as a matter of basic capacitance theory, a capacitor having very thin dielectric layers and many pairs of electrodes could have substantial capacitance despite being of miniature size with the active area of the electrodes being quite small.
Modern microcircuitry not only is well suited for miniature capacitors, but a further requirement of such capacitor applications is an ability to withstand high temperatures. In an electronic circuit, a capacitor could be subject to sustained temperatures of up to 125.degree.-150.degree. C. Even more demanding, circuit production techniques such as wave soldering could subject capacitors to temperatures beyond the melting point of solder, about 260.degree.-290.degree. C. for as long as 5 to 10 seconds.
It is an object of the invention to provide an improved capacitor concept, including the capacitor architecture itself, as well as the methods and apparatus for forming that architecture that produces a very small, miniature capacitor which nevertheless has practical levels of capacitance.
A further object is to provide a concept of the foregoing kind that can very economically produce multi layer structures such as capacitors, both in the sense of using limited amounts of materials as well as permitting high volume, high speed manufacturing as, for example, in the high speed manufacturing of capacitors. A related object in the instance of capacitors is to provide such a concept in which the electrical connections or leads can be easily and economically added to the individual capacitors, and the capacitor encapsulated without difficulty.
Another object is to provide a concept as characterized above that results in a capacitor capable of withstanding substantial temperatures such as the 260.degree.-290.degree. C. temperature encountered during the process of wave soldering. A collateral object is to provide a concept of this kind that could readily be mounted on the bottom or foil side of a circuit board so as to permit compaction of the required physical size of a circuit using such capacitors.
It is also an object to provide a concept of the above character that is not polarity sensitive, i.e., the capacitor is reversible. An accompanying object is to provide such a concept in which the capacitor fails open, in other words, the capacitor is self-healing rather than being subject to shorting out an entire electrical circuit.